Scrolling on Reddit and I came across an interesting perspective I hadn’t considered before. “Harry should have been in Slytherin! The hat said so!” is a take many people agree with, but a few people pointed out this:
Harry was the first to bring up Slytherin — “Not Slytherin” — and then, and only then, did the hat go (paraphrased), “Are you sure? You’d do well in Slytherin.”
Also, the hat brought up courage and a thirst for knowledge before Harry had even spoken. If we looked at the most baseline traits of the four houses, it sounds like Gryffindor and Ravenclaw were the ones the hat was considering more.
(Also also, and this is veering into more personal opinion, canon!Harry should not have been Slytherin because the story would have vastly changed. But that’s what fanfiction is for!)